README.md

Implement Stack using Queues

Solution 1

Two Queue

class MyStack {
    Queue<Integer> queue1;
    Queue<Integer> queue2;

    public MyStack() {
        queue1 = new LinkedList<>();
        queue2 = new LinkedList<>();
    }

    // O(n)
    public void push(int x) {
        queue2.add(x);
        while (!queue1.isEmpty()) {
            queue2.add(queue1.remove());
        }

        Queue<Integer> temp = queue1;
        queue1 = queue2;
        queue2 = temp;
    }

    public int pop() {
        return queue1.remove();
    }

    public int top() {
        return queue1.peek();
    }

    public boolean empty() {
        return queue1.isEmpty();
    }
}

Solution 2

One Queue

class MyStack {
    Queue<Integer> queue;

    /** Initialize your data structure here. */
    public MyStack() {
        queue = new LinkedList<>();
    }

    // O(n)
    public void push(int x) {
        queue.add(x);
        int size = queue.size();
        while (size != 1) {
            queue.add(queue.remove());
            size--;
        }
    }

    public int pop() {
        return queue.remove();
    }

    public int top() {
        return queue.peek();
    }

    public boolean empty() {
        return queue.isEmpty();
    }
}